Reduced-weight fuel cell plate with corrosion resistant coating

ABSTRACT

The disclosed embodiments provide a fuel cell plate. The fuel cell plate includes a substrate of electrically conductive material and a first outer layer of corrosion-resistant material bonded to a first portion of the substrate. To reduce the weight of the fuel cell plate, the electrically conductive material and the corrosion-resistant material are selected to be as light as practicable.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation patent application of U.S. patentapplication Ser. No. 12/759,933, filed Apr. 14, 2010 and titled“Reduced-Weight Fuel Cell Plate with Corrosion Resistant Coating,” nowU.S. Pat. No. 8,956,784, the disclosure of which is hereby incorporatedherein by reference in its entirety.

TECHNICAL FIELD

The present embodiments relate to power sources for electronic devices.More specifically, the present embodiments relate to techniques forreducing the weight of fuel cells for use with portable electronicdevices.

BACKGROUND

Fuel cells provide electrical power by converting a source fuel, such ashydrogen or a hydrogen-containing compound, into an electric current anda waste product by electrochemical means. In particular, a fuel cellcontains an anode, a cathode, and an electrolyte between the anode andcathode. Electricity may be generated by two chemical reactions withinthe fuel cell. First, a catalyst at the anode oxidizes the fuel toproduce positively charged ions and electrons. The electrolyte may allowions from the oxidation process to pass through to the cathode whileblocking passage of the electrons. The electrons may thus be used todrive a load connected to the fuel cell before recombining with the ionsand a negatively charged atom (e.g., oxygen) at the cathode to form awaste product such as carbon dioxide and/or water.

Because fuel cells are typically associated with low voltages (e.g.,0.5-0.7 volts), multiple fuel cells may be combined to form a fuel cellstack. For example, a fuel cell stack may contain a number of stackedbipolar plates. Each bipolar plate may provide an anode on one side anda cathode on the other side. To form fuel cells within the stack, thecatalyst and the electrolyte may be placed in between the bipolarplates. The fuel cells may then be connected in series to increase thevoltage of the fuel cell stack.

However, existing fuel cell stack architectures may have a number ofdisadvantages. First, each fuel cell may represent a single point offailure in a series-connected fuel cell stack. In addition, a fuel cellmay be subject to a number of failure modes, including accumulation ofnitrogen in the anode, poisoning of the catalyst, degradation of theelectrolyte, and/or water flooding in the anode or cathode.Consequently, the reliability of a fuel cell stack may decrease as thenumber of fuel cells in the fuel cell stack increases.

Second, bipolar plates for fuel cell stacks are typically manufacturedusing materials that are both conductive and corrosion-resistant, suchas stainless steel. However, the high density of such materials mayresult in heavy bipolar plates that restrict the use of fuel cell stacksin portable applications. For example, adoption of a fuel cell stackdesign as a power source for portable electronic devices may be hamperedby the weight of the resulting fuel cell stack, the majority of which isin stainless steel bipolar plates.

Hence, the use of fuel cells as power sources may be facilitated byimprovements in the reliability, weight, and/or size of fuel cellstacks.

SUMMARY

The disclosed embodiments provide a fuel cell plate. The fuel cell plateincludes a substrate of electrically conductive material and a firstouter layer of corrosion-resistant material bonded to a first portion ofthe substrate. To reduce the weight of the fuel cell plate, both theelectrically conductive material and the corrosion-resistant materialare selected to be as light as practicable.

In some embodiments, the fuel cell plate also includes a second outerlayer of solderable material bonded to a second portion of thesubstrate.

In some embodiments, the first outer layer and the second outer layerare simultaneously bonded to the substrate using a cladding technique.

In some embodiments, the fuel cell plate also includes a coating ofcorrosion-resistant solderable material over the second outer layer.

In some embodiments, the second portion of the substrate and the secondouter layer correspond to a solder tab for the fuel cell plate.

In some embodiments, the fuel cell plate also includes acorrosion-resistant sealant applied to an exposed edge of the substrate.

In some embodiments, the corrosion-resistant sealant is applied using awelding technique, a molding technique, or a coating technique.

In some embodiments, the first outer layer is bonded to the firstportion of the substrate using a cladding technique, a sputteringtechnique, a spraying technique, a plating technique, or a coatingtechnique.

In some embodiments, the first portion of the substrate and the firstouter layer correspond to an electrode for a fuel cell.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic of a system in accordance with the disclosedembodiments.

FIG. 2 shows a fuel cell plate in accordance with the disclosedembodiments.

FIG. 3 shows a cross-sectional view of a fuel cell plate in accordancewith the disclosed embodiments.

FIG. 4 shows a flowchart illustrating the process of manufacturing afuel cell plate in accordance with the disclosed embodiments.

FIG. 5 shows a fuel cell plate with a co-molded gasket in accordancewith the disclosed embodiments.

FIG. 6 shows a portable electronic device in accordance with thedisclosed embodiments.

In the figures, like reference numerals refer to the same figureelements.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled inthe art to make and use the embodiments, and is provided in the contextof a particular application and its requirements. Various modificationsto the disclosed embodiments will be readily apparent to those skilledin the art, and the general principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the present disclosure. Thus, the present invention is notlimited to the embodiments shown, but is to be accorded the widest scopeconsistent with the principles and features disclosed herein.

The data structures and code described in this detailed description aretypically stored on a computer-readable storage medium, which may be anydevice or medium that can store code and/or data for use by a computersystem. The computer-readable storage medium includes, but is notlimited to, volatile memory, non-volatile memory, magnetic and opticalstorage devices such as disk drives, magnetic tape, CDs (compact discs),DVDs (digital versatile discs or digital video discs), or other mediacapable of storing code and/or data now known or later developed.

The methods and processes described in the detailed description sectioncan be embodied as code and/or data, which can be stored in acomputer-readable storage medium as described above. When a computersystem reads and executes the code and/or data stored on thecomputer-readable storage medium, the computer system performs themethods and processes embodied as data structures and code and storedwithin the computer-readable storage medium.

Furthermore, methods and processes described herein can be included inhardware modules or apparatus. These modules or apparatus may include,but are not limited to, an application-specific integrated circuit(ASIC) chip, a field-programmable gate array (FPGA), a dedicated orshared processor that executes a particular software module or a pieceof code at a particular time, and/or other programmable-logic devicesnow known or later developed. When the hardware modules or apparatus areactivated, they perform the methods and processes included within them.

FIG. 1 shows a schematic of a system in accordance with the disclosedembodiments. The system may provide a power source to a load 108, suchas a mobile phone, laptop computer, portable media player, and/orperipheral device. As shown in FIG. 1, the system includes a number offuel cells 110, 112, 114, 116, 118, 120, 122, and 124 arranged in a fuelcell stack 102.

Fuel cells 110-124 may correspond to electrochemical cells that converta source fuel into electric current and a waste product. In particular,fuel cells 110-124 may be proton exchange membrane (PEM) fuel cells thatuse hydrogen as a fuel. The hydrogen may be catalytically split intoprotons and electrons at the anode of each PEM fuel cell. The protonsmay pass through an electrically insulating membrane electrode assembly(MEA) 101 to the cathode of the PEM fuel cell, while the electrons maytravel through a load 108 to the cathode. The protons and electrons maythen react with oxygen atoms at the cathode to form water molecules as awaste product. Alternatively, fuel cells 110-124 may correspond to solidoxide fuel cells, molten carbonate fuel cells, direct methanol fuelcells, alkaline fuel cells, phosphoric acid fuel cells, and/or othertypes of fuel cells.

Because individual fuel cells 110-124 may generate a voltage (e.g.,0.5-0.7 volts for PEM fuel cells) that is too low to drive mostcomponents (e.g., processors, peripheral devices, backlights, displays,Universal Serial Bus (USB) ports, etc.) in load 108, fuel cells 110-124may be electrically connected in a series configuration. For example, aset of 25 PEM fuel cells may be connected in series within fuel cellstack 102 to increase the voltage of fuel cell stack 102 to roughly12.5-17.5 volts. The increased voltage may then be used to drivecomponents with operating voltages at or below the voltage of fuel cellstack 102.

Furthermore, fuel cells 110-124 may be assembled into fuel cell stack102 to conserve space and/or provide a packaged power source for drivingload 108. To form fuel cells 110-124 within fuel cell stack 102, layersof MEA 101 may be sandwiched between a set of stacked bipolar plates.Each bipolar plate may include one side that functions as a cathode forone fuel cell and another side that functions as an anode for anadjacent fuel cell.

The cathode side of the bipolar plate may be corrugated or otherwisephysically and/or chemically treated to facilitate a relatively uniformdistribution of oxygen across the plate. The oxygen may then combinewith the protons that have passed through the MEA and the electrons thathave traveled through load 108 to form water, a waste product. The anodeside of the bipolar plate may be smooth or otherwise physically and/orchemically treated to facilitate a relatively uniform distribution ofhydrogen across the plate. For example, uniform hydrogen distributionmay be facilitated by the etching of narrow and/or shallow channels intothe anode side of a bipolar plate. In addition, the bipolar plate may bemade from a conductive, corrosion-resistant material such as stainlesssteel to enable the electrodes to conduct electric current whileresisting corrosion from water vapor at the cathode.

However, the creation of fuel cells 110-124 from bipolar plates made ofhigh-density materials such as stainless steel may increase the size,weight, and/or cost of fuel cell stack 102. For example, stainless steelbipolar plates may be responsible for 80% of the weight and 30% of thecost of fuel cell stack 102. As a result, fuel cell stack 102 may bedifficult to use in portable applications (e.g., powering portableelectronic devices).

To facilitate the use of fuel cell stacks as power sources for portableelectronic devices, the disclosed embodiments provide a reduced-weightfuel cell plate that is lighter, less resistive, and/or more thermallyconductive than comparable bipolar plates made of high-densitymaterials. Because fuel cell stacks containing the reduced-weight fuelcell plate have similar weight savings over fuel cell stacks containingheavier bipolar plates, the lighter fuel cell stacks may be moresuitable for use as power sources for portable electronic devices. Asdiscussed below, the lowered resistance and/or increased thermalconductivity may further facilitate the parallel connection of fuelcells 110-124 while improving the consistency of operation, powerdensity, and/or acoustic noise of fuel cell stack 102.

As shown in FIG. 2, the fuel cell plate includes two portions 202

204. Portion 202 may correspond to an electrode for a fuel cell, such asa PEM fuel cell. For example, the top of portion 202 may provide ananode for a fuel cell, while the bottom of portion 202 may be corrugatedto provide a cathode for an adjacent fuel cell.

Portion 204 may correspond to a solder tab for the fuel cell plate. Inparticular, portion 204 may be soldered to a printed circuit board (PCB)to allow electric current to flow between portion 202 and the PCB. Theelectric current may then be used to power a load (e.g., load 108 ofFIG. 1) and/or monitor the health of the fuel cell stack containing thefuel cell plate. For example, a component on the PCB may use theelectrical connection between portion 202 and the PCB to monitor thevoltage of a fuel cell containing portion 202. The component may alsouse the monitored voltage to improve reliability in the fuel cell stack.In particular, changes in the voltage may alert the component todegradation in the fuel cell and allow the component to remedy thedegradation before the fuel cell fails and disables the fuel cell stack.

As mentioned previously, the fuel cell plate may be made from anelectrically conductive, corrosion-resistant material such as stainlesssteel. On the other hand, the low solderability of stainless steel maybe incompatible with the use of portion 202 as a solder tab. As aresult, portions 202-204 may utilize different materials to performtheir respective functions. For example, stainless steel may be used toenhance the corrosion resistance of portion 202, while copper may beused to facilitate the creation of a reliable solder joint betweenportion 204 and the PCB.

In addition, the use of other materials in the fuel cell plate mayreduce the weight and/or resistance of the fuel cell plate whilemaintaining the functionality of portions 202-204. More specifically, avariety of materials with different material properties may be layeredand/or bonded to form the fuel cell plate. As shown in thecross-sectional view of FIG. 3, the fuel cell plate includes a layer ofsubstrate 302, a first outer layer 304, and a second outer layer 306.The fuel cell plate may also include a first coating 308 over firstouter layer 304 and a second coating 310 over second outer layer 306.First outer layer 304 and first coating 308 may be in portion 202, whilesecond outer layer 306 and second coating 310 may be in portion 204.

First and second outer layers 304-306 and first and second coatings308-310 may include material properties that facilitate the respectiveuses of portions 202-204. As discussed above, portion 202 may correspondto a cathode and/or an anode for a fuel cell. Consequently, aconductive, corrosion-resistant material such as stainless steel ortitanium may be used in first outer layer 304 to provide corrosionresistance to water vapor generated during fuel cell operation. Thecorrosion resistance of portion 202 may be extended with a first coating308 of a material that is more corrosion resistant than the material offirst outer layer 304, such as titanium nitride and/or gold. Asdiscussed below with respect to FIGS. 4-5, first coating 308 may also beapplied to an exposed edge of substrate 302 to prevent substrate 302from coming into direct contact with water.

On the other hand, portion 204 may function as a solder tab. As aresult, second outer layer 306 may be made of a solderable material suchas copper, beryllium copper, and/or nickel silver. Because second outerlayer 306 may have low corrosion resistance, a second coating 310 of asolderable, corrosion-resistant material such as tin or gold may be usedto minimize corrosion of second outer layer 306 before the solderoperation.

To reduce weight and/or resistance in the fuel cell plate, substrate 302may contain an electrically conductive material that is lighter than thecorrosion-resistant material of first outer layer 304. For example, agrade 316L stainless steel outer layer may be used with a substrate suchas aluminum, beryllium, beryllium aluminum, and/or beryllium copper tocreate a fuel cell plate that is lighter, less resistive, and/or morethermally conductive than a fuel cell plate containing only stainlesssteel. Additional savings in weight and/or resistance may be achieved byforming holes, channels, and/or cavities within substrate 302. Forexample, gaps in substrate 302 may be created by placing multiplenon-touching and/or partially touching pieces of aluminum in between twosheets of stainless steel.

In one or more embodiments, the fuel cell plate is created by bondingouter layers 304-306 to substrate 302 and applying coatings 308-310 overouter layers 304-306. In particular, a cladding technique, sputteringtechnique, spraying technique, and/or plating technique may be used tofuse the surfaces of outer layers 304-306 to substrate 302 and/ordeposit coatings 308-310 onto outer layers 304-306. As discussed belowwith respect to FIG. 4, an efficient manufacturing process for the fuelcell plate may be enabled through the targeted and/or concurrentexecution of one or more techniques.

FIG. 4 shows a flowchart illustrating the process of manufacturing afuel cell plate in accordance with the disclosed embodiments. In one ormore embodiments, one or more of the steps may be omitted, repeated,and/or performed in a different order. Accordingly, the specificarrangement of steps shown in FIG. 4 should not be construed as limitingthe scope of the embodiments.

To begin with, a first outer layer of corrosion-resistant material isarranged over a first portion of a substrate of electrically conductivematerial (operation 402) that is lighter than the corrosion-resistantmaterial, and a second outer layer of solderable material is arrangedover a second portion of the substrate (operation 404). The firstportion of the substrate and the first outer layer may correspond to anelectrode for a fuel cell, while the second portion of the substrate andthe second outer layer may correspond to a solder tab for the fuel cellplate. Next, the first outer layer and the second outer layer aresimultaneously bonded to the substrate using a cladding technique(operation 406). The cladding technique may bond the outer layers to thesubstrate by pressing or rolling the layers together under highpressure.

For example, a sheet of grade 316L stainless steel may be placedside-by-side with a narrow sheet of copper so that the edges of the twosheets are touching. The two sheets of metal may then be pressed and/orrolled to fuse the joint line between the sheets. Alternatively,intimate contact between the edges may be established with a weldingtechnique, such as electron beam welding, friction stir welding,ultrasonic welding, laser welding, and/or resistance welding. A sheet ofaluminum may be placed on top of the joined sheets, and another joinedsheet of aluminum and copper may be placed on top of the aluminum. Inother words, the joined sheets of stainless steel and copper maycorrespond to outer layers that flank an aluminum substrate. Finally,the three sheets may be rolled under high pressure to bond the stainlesssteel and copper to the aluminum. Methodical application of cladding maythus facilitate the efficient manufacturing of the fuel cell plate byenabling the simultaneous bonding of two separate outer layers todifferent parts of a substrate.

After the outer layers are bonded to the substrate, the corrosionresistance of the fuel cell plate may be increased by applying a coatingof corrosion-resistant solderable material over the second outer layer(operation 408). Moreover, the coating may be applied during thecladding technique to further facilitate the efficient creation of thefuel cell plate. Continuing with the above example, acorrosion-resistant coating of tin may be deposited over the copperouter layer using a laser-cladding technique immediately after thesheets are clad by a roller.

The fuel cell plate is then cut to the desired geometry (operation 410).For example, the fuel cell plate may be cut out of a rectangular sheetof layered metal into the shape shown in FIG. 2. Surface features suchas grooves, dimples, and/or channels may also be added to one or bothsides of the fuel cell plate to facilitate use of the fuel cell plate asan electrode in a fuel cell. Along the same lines, holes may be drilledthrough the fuel cell plate to enable mounting of the fuel cell plateand/or facilitate draining or evaporation of water vapor during fuelcell operation.

Finally, a corrosion-resistant sealant may be applied to an exposed edgeof the substrate (operation 412) to seal the substrate within one ormore corrosion-resistant layers. The exposed edge may be found along theperimeter of the fuel cell plate and/or around one or more holes thatspan the thickness (e.g., layers) of the fuel cell plate. To apply thecorrosion-resistant sealant, a welding technique, molding technique,and/or coating technique may be used. For example, a strip ofcorrosion-resistant material (e.g., stainless steel) may be weldedaround the perimeter of the fuel cell plate. Alternatively, a coating(e.g., first coating 308 of FIG. 3) of corrosion-resistant material suchas titanium nitride may be deposited over the electrode portion of thefuel cell plate, including the exposed edge of the substrate.

As shown in FIG. 5, the corrosion-resistant sealant may also be appliedin the form of one or more co-molded gaskets 502-504. Gaskets 502-504may cover one or more edges of the fuel cell plate with an elastomersuch as silicone. In addition, gaskets 502-504 may be co-molded onto thefuel cell plate to seal off exposed edges of the substrate both alongthe perimeter of the fuel cell plate and around holes that span thelayers of the fuel cell plate. Gaskets 502-504 may also include channelsand/or passages to allow water vapor to escape from the surface of thefuel cell plate if the elastomer covers the cathode side of the fuelcell plate.

The above-described fuel cell plate can generally be used in any type ofelectronic device. For example, FIG. 6 illustrates a portable electronicdevice 600 which includes a processor 602, a memory 604 and a display608, which are all powered by a power source 606. Portable electronicdevice 600 may correspond to a laptop computer, mobile phone, personaldigital assistant (PDA), portable media player, digital camera, and/orother type of compact electronic device.

Power source 606 may correspond to a fuel cell stack that includes a setof fuel cell plates. Each fuel cell plate may contain a substrate ofelectrically conductive material and a first outer layer ofcorrosion-resistant material bonded to a first portion of the substrate.The fuel cell plate may also contain a second outer layer of solderablematerial bonded to a second portion of the substrate, a coating ofcorrosion-resistant solderable material over the second outer layer,and/or a corrosion-resistant sealant applied to an exposed edge of thesubstrate.

Because both the electrically conductive material and/or thecorrosion-resistant material are chosen to be as light as practicable,the fuel cell stack may be lighter than fuel cell stacks of fuel cellplates that contain only the corrosion-resistant material. The reducedweight may additionally facilitate the use of the fuel cell stack inpowering portable electronic device 600 over heavier fuel cell stacks.Furthermore, the use of materials such as aluminum for the substrate maylower the resistance and increase the thermal conductivity of the fuelcell plates over stainless steel bipolar plates. The lower resistancemay reduce the electrical losses of the fuel cell stack and, in turn,facilitate the connection of the fuel cells in a parallel configurationthat produces a higher amount of current than a series configuration ofthe same fuel cells. In addition, the increased thermal conductivity mayimprove the consistency of operation and/or power density of the fuelcell stack while reducing acoustic noise generated during operation ofthe fuel cell stack.

The foregoing descriptions of various embodiments have been presentedonly for purposes of illustration and description. They are not intendedto be exhaustive or to limit the present invention to the formsdisclosed. Accordingly, many modifications and variations will beapparent to practitioners skilled in the art. Additionally, the abovedisclosure is not intended to limit the present invention.

What is claimed is:
 1. A fuel cell plate, comprising: a substrate ofelectrically conductive material, the substrate having a first portionand a second portion; an electrode portion formed on the first portionof the substrate, the electrode portion comprising: a first outer layerincluding a first corrosion-resistant material having a higher densitythan the substrate of electrically conductive material and bonded to thefirst portion of the substrate; and a first coating of a secondcorrosion-resistant material bonded to at least a portion of an outersurface of the first outer layer; and a solder tab formed on the secondportion of the substrate, the solder tab comprising: a second outerlayer comprising a solderable material, the solderable material beingdifferent from the electrically conductive material of the substrate,the second outer layer bonded to the second portion of the substrate;and a second coating of solderable, corrosion-resistant material, thesolderable, corrosion-resistant material being different from saidsecond corrosion-resistant material of the first coating, said secondcoating bonded to at least a portion of an outer surface of the secondouter layer.
 2. The fuel cell plate of claim 1, further comprising: acorrosion-resistant sealant formed on an edge of the substrate ofelectrically conductive material.
 3. The fuel cell plate of claim 1,wherein the electrode portion comprises: an anode portion on a firstside of the substrate; and an cathode portion on a second side of thesubstrate that is opposite to the first side.
 4. The fuel cell plate ofclaim 3, wherein the cathode portion is corrugated.
 5. The fuel cellplate of claim 1, further comprising: a gasket formed around at leastpart of an edge of the substrate of electrically conductive material. 6.The fuel cell plate of claim 5, wherein the gasket is co-molded around aperimeter of the fuel cell plate.
 7. The fuel cell plate of claim 5,wherein the gasket defines at least one passage for water vapor toescape from the electrode portion of the fuel cell plate.
 8. A fuel cellstack, comprising: a set of fuel cells arranged in a stack; and a set ofelectrically insulating membrane electrode assembly layers arranged inthe stack and separating each fuel cell from an adjacent fuel cell ofthe set of fuel cells, wherein each fuel cell comprises: a substrate ofelectrically conductive material; an electrode portion formed on a firstportion of the substrate, the electrode portion comprising: a firstouter layer including a first corrosion-resistant material having ahigher density than of electrically conductive material; and a firstcoating of a second corrosion-resistant material bonded to at least aportion of an outer surface of the first outer layer; and a solder tabformed on a second portion of the substrate, the solder tab comprising:a second outer layer comprising a solderable material, the solderablematerial being different from the electrically conductive material ofthe substrate; and a second coating of solderable, corrosion-resistantmaterial, the solderable, corrosion-resistant material being differentfrom said second corrosion-resistant material of the first coating, saidsecond coating bonded to at least a portion of an outer surface of thesecond outer layer.
 9. The fuel cell stack of claim 8, wherein the setof fuel cells are electrically connected in series.
 10. The fuel cellstack of claim 8, wherein each electrically insulating membraneelectrode assembly layer of the set of electrically insulating membraneelectrode assembly layers is configured to pass protons between adjacentfuel cells.
 11. The fuel cell stack of claim 8, further comprising: acorrosion-resistant sealant formed on an edge of the substrate ofelectrically conductive material.
 12. The fuel cell stack of claim 8,wherein the electrode portion comprises: an anode portion on a firstside of the substrate; and a cathode portion on a second side of thesubstrate that is opposite to the first side.
 13. The fuel cell plate ofclaim 12, wherein the cathode portion is corrugated.
 14. The fuel cellstack of claim 8, further comprising: a gasket formed around at leastpart of an edge of the substrate of electrically conductive material.15. The fuel cell stack of claim 14, wherein the gasket is co-moldedaround a perimeter of a fuel cell of the set of fuel cells.
 16. The fuelcell stack of claim 14, wherein the gasket defines at least one passagefor water vapor to escape from the electrode portion of a fuel cell ofthe set of fuel cells.